Inventory: Add failing test case for itemstack NBT duplication

tests/phpunit/inventory/BaseInventoryTest.php

@@ -0,0 +1,59 @@
+<?php
+
+/*
+ *
+ *  ____            _        _   __  __ _                  __  __ ____
+ * |  _ \ ___   ___| | _____| |_|  \/  (_)_ __   ___      |  \/  |  _ \
+ * | |_) / _ \ / __| |/ / _ \ __| |\/| | | '_ \ / _ \_____| |\/| | |_) |
+ * |  __/ (_) | (__|   <  __/ |_| |  | | | | | |  __/_____| |  | |  __/
+ * |_|   \___/ \___|_|\_\___|\__|_|  |_|_|_| |_|\___|     |_|  |_|_|
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * @author PocketMine Team
+ * @link http://www.pocketmine.net/
+ *
+ *
+*/
+
+declare(strict_types=1);
+
+namespace pocketmine\inventory;
+
+use PHPUnit\Framework\TestCase;
+use pocketmine\item\Item;
+use pocketmine\item\ItemFactory;
+
+class BaseInventoryTest extends TestCase{
+
+	public static function setUpBeforeClass(){
+		ItemFactory::init();
+	}
+
+	public function testAddItemDifferentUserData() : void{
+		$inv = new class extends BaseInventory{
+			public function getDefaultSize() : int{
+				return 1;
+			}
+			public function getName() : string{
+				return "";
+			}
+		};
+		$item1 = ItemFactory::get(Item::ARROW, 0, 1);
+		$item2 = ItemFactory::get(Item::ARROW, 0, 1)->setCustomName("TEST");
+
+		$inv->addItem(clone $item1);
+		self::assertFalse($inv->canAddItem($item2), "Item WITHOUT userdata should not stack with item WITH userdata");
+		self::assertNotEmpty($inv->addItem($item2));
+
+		$inv->clearAll();
+		self::assertEmpty($inv->getContents());
+
+		$inv->addItem(clone $item2);
+		self::assertFalse($inv->canAddItem($item1), "Item WITH userdata should not stack with item WITHOUT userdata");
+		self::assertNotEmpty($inv->addItem($item1));
+	}
+}